ABSTRACT
Delayed type hypersensitivity skin testing to tetanus toxoid was performed in 498 healthy Thai children. The subjects were 230 males and 268 females. The ages at testing were 2, 4, 6, 9, 15, 18 and 48 months and the number of subjects were 98, 94, 82, 77, 43, 70 and 34, respectively. The study was performed by intradermal injection of 0.1 ml. of tetanus toxoid (20 Lf/ml) 0.1 ml at the volar surface of left forearm. An indurations of 5 mm. or greater at 72 hours was considered a positive result. The positive result in each group was 7.14, 30.85, 76.82, 98.7, 90.7, 97.14 and 94.12 percent respectively. The mean induration size in each group was 2.16, 3.74, 6.46, 9.79, 10.42, 9.07 and 9.76 mm., respectively. The results of the study showed no difference between the sexes. Positive skin tests to tetanus toxoid were correlated to the number of previous DPT immunizations. No significant adverse reaction was found. These results indicate that tetanus toxoid skin testing is safe and yields highly positive results in children who have been immunized with tetanus toxoid. It should be used as an antigen for delayed type hypersensitivity skin testing as PPD, mumps, monilia, trichophyton and streptokinase-streptodornase.